Those stale NFS files are very stubborn to remove. At least I have not been clever enough to do it. My only solution for this problem is to delete the debian image and start over. Then, when you start downloading programs, always do apt-get clean so that the file system does not get clogged up. To see for yourself how much memory is being used up, do a df while in debian chroot after a download. Then do an apt-get clean. df again and there should be a noticeable increase in memory. Finally, when you have downloaded enough stuff, back up the image so you don't have to start from the beginning again. Can't claim this will fix things for you but I have not had a problem with reboots or stale NFS files since I have followed this protocol.